They have spent years working school boards, with only minimal success. Now critics of evolution are turning to a higher authority: state legislators.
In a bid to shape biology lessons, they are promoting what they call "academic freedom" bills that would encourage or require public-school teachers to cast doubt on a cornerstone of modern science.
A handful of states have considered such bills in recent years, but backers are now organizing a national movement, with high-profile help from actor Ben Stein. His new documentary, "Expelled," argues that educators suffer reprisals if they dare question evolution; in an attempt to spur action, he has held private screenings for legislators, including a recent showing in the Missouri statehouse.
The academic-freedom bills now in circulation vary in detail. Some require teachers to critique evolution. Others let educators choose their approach -- but guarantee they won't be disciplined should they decide to build a case against Darwin.
The common goal: To expose more students to articles and videos that undercut evolution. Most of this material is produced by advocates of intelligent design or Biblical creationism, the belief that God created man in his present form.
"The creationist legal strategy has gotten more and more sophisticated," said Eugenie Scott, director of the National Center for Science Education, a nonprofit that promotes the teaching of evolution.
Both houses of the Florida legislature passed academic freedom bills this month, but it is unclear whether backers can reconcile the two versions before the spring session closes Friday. If not, they will have to try again next year. Prospects may be better in Louisiana, where the state Senate this week unanimously approved a bill ensuring that teachers can go beyond the biology textbook to raise criticisms of evolution. Similar bills have just been introduced in Alabama and Michigan and this week passed through a house committee in Missouri.
"It shouldn't be a crime for teachers to give the best evidence for evolutionary theory and then, if they want, spend a day saying, 'Some people are raising questions,'" said John West, a senior fellow at the Discovery Institute.
The nonprofit institute, based in Seattle, promotes the theory that life was created by an unknown designer, possibly divine. It recently launched a petition drive to spur more states to take up such bills.
The legislative push builds on an emerging strategy developed by conservative Christians who consider evolution ungodly and a small group of scientists who find it implausible.
Over the last decade, these skeptics tried repeatedly to push Darwin out of -- or wedge alternatives to evolution into -- public-school science curricula. Those efforts largely failed, rebuffed by the courts or rejected by voters.
So activists regrouped. Their new tactic: Embrace lessons on evolution. In fact, insist students deserve to learn more -- including classes that probe the theory for weakness. They believe -- and their opponents agree -- that this approach will prove more acceptable to the public and harder to challenge in court.
Those promoting the new bills emphasize that academic freedom doesn't mean biology teachers can read aloud from the Book of Genesis. "This doesn't bring religion into the classroom," said Florida state Rep. D. Alan Hays, a Republican.
The bills typically restrict lessons to "scientific" criticism of evolution, or require that critiques be presented "in an objective manner," or approved by a local school board.
Evolution's defenders respond that there are no credible scientific critiques of evolution, any more than there are credible alternatives to the theory of gravity. The fossil record, DNA analysis and observations of natural selection confirm Darwin's hypothesis that all life on Earth evolved from a common ancestor over four billion years.
In the scientific community, while there may be debate about the details, the grand sweep of evolution is unassailable. "There's no controversy," said Jay Labov, a senior adviser for education and communication with the National Academy of Sciences.
But Gallup polls consistently show that nearly half of American adults reject evolution. A third are upset that schools teach it, according to Gallup.
Several states, including South Carolina and Pennsylvania, have passed science standards requiring students to think critically about evolution.
Ms. Scott, of the science-education group, regards the academic-freedom bills as a more serious threat to evolution education because they give teachers so much latitude. "This is basically a get-out-of-jail-free card for creationist teachers," she said.
So far, few teachers have come forward in favor of these bills. The Florida Education Association, which represents 140,000 teachers, opposes the concept.
Doug Cowan, a public-school biology teacher, said his colleagues are often afraid to speak out.
Mr. Cowan said he tells students: "I'm going to give you the evidence for evolution and the evidence against, and let you decide." For instance, he'll mention Darwin's observation that finches evolve different-shaped beaks to suit different ecosystems. Then he'll add that you don't see a finch changing into another species.
Asked what evidence he presents to bolster evolution, Mr. Cowan paused. "I don't have any," he said.
Mr. Cowan's principal said that teachers are not supposed to veer from the approved textbooks. That's why Mr. Cowan would like a legal guarantee he can teach as he sees fit.
"This is America," Mr. Cowan said. "My gosh. Why walk on eggshells?"
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